Light stimulating and collecting methods and apparatus for storage-phosphor image plates

ABSTRACT

Methods and apparatus are described for retrieving information from a storage medium. A first portion of the surface of the storage medium is exposed to stimulating light which diffuses in the storage medium under a second portion of the surface adjacent the first portion. The second portion of the surface is shielded from exposure to the stimulating light. Stimulated light corresponding to the information is received with at least one detector positioned to receive the stimulated light via the second portion of the surface of the storage medium. The stimulated light is released from the storage medium in response to the stimulating light diffused under the second portion of the surface.

RELATED APPLICATION DATA

The present application claims priority from and is a continuation ofU.S. patent application Ser. No. 11/462,666 filed Aug. 4, 2006 (AttorneyDocket No. SAY1P004D2) which is a divisional of U.S. patent applicationSer. No. 10/789,547 filed Feb. 26, 2004 (Attorney Docket No.SAY1P004D1), which claims priority from U.S. patent application Ser. No.09/887,543 filed Jun. 21, 2001 (Attorney Docket No. SAY1P004), now U.S.Pat. No. 6,800,870, which claims priority from U.S. ProvisionalApplication No. 60/257,622 filed Dec. 20, 2000 (Attorney Docket No.SAY1P004P), the entire disclosures of each of which is incorporatedherein by reference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates to the field of digital radiography andmore specifically to methods and apparatus for obtaining an electricalrepresentation of a radiation image using a storage-phosphor imageplate.

In the field of digital radiography a variety of methods have emerged.One such method is based on capturing the prompt-emitting light of aconventional phosphor screen with an image intensifier, a flat paneldetector, or a CCD camera. Another method described in U.S. Pat. No.3,859,527 (incorporated herein by reference for all purposes) uses astorage-phosphor plate for image detection. After being exposed tox-rays, the storage-phosphor plate is stimulated with an appropriatelight source and the image recorded on the plate is read out.

Various methods for reading stored images from storage-phosphor plateshave been proposed. A first method relies on a laser scanning mechanismthat stimulates one pixel at a time and collects the photo-stimulatedlight with a photomultiplier. Unfortunately, because only one pixel isread at a time, the readout time for a typical storage-phosphor plate isunacceptably long.

In addition, the laser scanning mechanism necessary to stimulate onepixel at a time on a 14″×17″ phosphor plate is very large and complex.The stimulating laser pencil beam must remain well focused on the plateand must scan it from side to side and top to bottom with perfectaccuracy. The typical size of a system for reading images from 14″×17″storage-phosphor plates is close to the size of a householdrefrigerator.

Another problem relates to interplay between the dimension of thestimulating laser pencil beam on the plate (which dictates the spatialresolution of the overall reading apparatus) and the efficiency withwhich light released from the storage medium is collected. The largerthe laser spot on the plate, the lower the resolution. As a result,typical medical storage-phosphor plate readers require the laser spotdiameter to be less than 200 microns. The stimulated area of thestorage-phosphor plate emits light corresponding to the intensity of thestored image at this particular location. The storage-phosphor materialis therefore chosen to have the wavelength of stimulated light differentfrom the wavelength of stimulating light so as to allow for selectivecollection of the stimulated light and complete rejection of thestimulating light. An optical filter is also typically used to rejectthe stimulating light and transmit the stimulated light. The opticalfilter is positioned between the plate and the photomultiplier.Ingenious light collectors have been envisioned to allow for maximumcollection of the stimulated light. However, it is very difficult toachieve high collection efficiency since the stimulating light path getsin the way of the stimulated light collection device.

In addition, the stimulated light emits in all directions due to theturbid nature of the storage phosphor plate, which makes it even moredifficult to collect. Conventional storage-phosphor plates are made ofpowder phosphor deposited on a plastic substrate. The phosphor materialis granular and white, which makes the powder an almost ideal Lambertianemitter and reflector. The stimulating light from the laser beam isminimally absorbed in the plate, and mostly diffused by the phosphorgranules to neighboring granules creating a spread of the laser spot onthe plate. This effect results in a reduction of the spatial resolutionof the plate reading system, since the region surrounding the laser spoton the plate is also stimulated.

The stimulated light created in the powder phosphor is also diffused inthe plate before it reaches the surface where it can be collected. Theamount of lateral diffusion of the stimulating light, and of thestimulated light, in the plate is a function of the size of the phosphorgranules and the binder material. It is also determined by the thicknessof the plate. Several techniques have been proposed to optimize thethickness of the plate and the size of the phosphor granules to achievemaximum performance. Thick phosphor layers are used to maximize theabsorption of high energy x-rays at the expense of the spatialresolution. Thinner phosphor layers are used to maximize spatialresolution for lower energy x-ray applications. Additional optimizationis achieved by placing a special layer underneath the phosphor layer,which can absorb the stimulating light and reflect the stimulated lightback to the front surface. Unfortunately, because of a variety oftradeoffs, none of the previous techniques addressing the spatialresolution issues of storage-phosphor based systems has been universallyeffective.

For example, attempts have been made to utilize storage plates which arenot made of powder phosphor, but rather of single crystal phosphor.These clear plates can potentially achieve higher spatial resolutionsince no light diffusion occurs in them, but they are very difficult tomanufacture and extremely sensitive to scratches and mishandling.

On the other hand, with conventional powder phosphor plates, laser-basedscanning systems require complex and sub-optimal tradeoffs betweenspatial resolution, bleaching ratio (i.e., readout efficiency), andreadout speed. The maximum readout time is often dictated by theapplication (typically less than one minute for medical readers). Therequired spatial resolution limits the stimulating laser power (toostrong of a laser beam creates too large of a spot) and, as a result,only a fraction of the available stimulated light is read out (i.e.,partial bleaching). These tradeoffs result in a degradation of imagequality (lower Detective Quantum Efficiency, i.e., DQE) since not allthe information is read out of the plate. Moreover, additional stepshave to be taken to erase the plate (to remove the unread information)before it is reused. Such erasures are typically achieved throughintense exposure under bright fluorescent tubes.

Whereas the storage-phosphor plates themselves are ideal replacements tofilm-screen combinations, currently available laser-based scanningsystems are far from ideal. To address at least some of thedisadvantages of such systems, attempts have been made to replace thepixel-by-pixel scanning mechanism with a linescan mechanism or atwo-dimensional capture device. Various linescan mechanisms have beenproposed in which the laser pencil beam is replaced by a laser fan beamand the photomultiplier is replaced by a one-dimensional array ofphotodetectors. The idea behind such a mechanism, is to read thestorage-phosphor plate one line at the time rather than one pixel at atime, thus allowing for a much faster readout time as well as a muchsimpler and smaller scanning mechanism, i.e., only one-axis mechanicalscanning is necessary instead of two-axis scanning.

The theoretical advantages of linescanning over pixel-by-pixel scanningare clear, but the practical implementation of the stimulating fan beamand the associated collecting optics is extremely challenging. Unlikethe pixel-by-pixel scanning scheme where the collecting optics arenon-imaging, most linescanning schemes require the collecting optics notonly to collect as much light as possible, but also image the surface ofthe plate onto the photodetector line array with suitable resolution.Such techniques also typically require the stimulating light to beconfined to an area of the plate smaller than the area imaged onto thephotodetector line array in order to guarantee that no stimulated lightis lost in the process. These two requirements are very difficult toachieve with conventional techniques as evidenced by the fact that nolinescanning plate reader is yet commercially available.

Numerous designs have been proposed, some relying on traditional optics(e.g., U.S. Pat. No. 5,747,825 the entire disclosure of which isincorporated herein by reference), but most assuming that traditionaloptics are not practical to efficiently image the surface of a plateonto a photodetector line array. In these designs, maximum collectionefficiency is achieved by placing the photodetector line array in closeproximity to the plate, with no conventional lens in between. Somedesigns suggest the use of a fiber-optic faceplate between the plate andthe photodetector line array presumably to overcome certain mechanicalissues related to the array bond wires.

In any case, high collection efficiency and high resolution may beachieved without a traditional lens provided that the linear array is indirect contact with the plate or that the distance between the plate andthe linear array is kept to a strict minimum. This constraint creates aserious challenge as far as stimulating the area right underneath thelinear array. A small gap can be placed between the plate and the lineararray to let the stimulating light pass through, but since the plate hasa Lambertian emission, this has a catastrophic effect on the collectionefficiency and spatial resolution of the system.

Several solutions have been proposed to solve this issue. One set ofsolutions, proposed by Hosoi (U.S. Pat. No. 4,880,987 incorporatedherein by reference), Leblans (European Patent No. 1014684 incorporatedherein by reference) and Schiebel (U.S. Pat. No. 4,953,038 incorporatedherein by reference), consists of utilizing a transparent phosphor plate(as opposed to a conventional turbid phosphor plate) and placing thestimulating light source on the side of the plate opposite the lineararray. In this configuration, no gap is necessary between the plate andthe linear array and maximum light collection efficiency and spatialresolution can be achieved. However, as discussed above, the cost ofproducing and handling this type of phosphor plate can be prohibitivelyexpensive.

Another solution proposed by Kawajiri (U.S. Pat. No. 4,922,103incorporated herein by reference) consists of placing the stimulatinglight source on the side of the linear array opposite the plate. Thisassumes that the linear array is completely transparent at thewavelength of stimulating light (so as to let the stimulating light passthrough the linear array to stimulate the plate), and highly absorbingat the wavelength of the stimulated light (so as to convert thestimulated light into electrical signal). Another solution proposed byCarter (U.S. Pat. No. 4,933,558 incorporated herein by reference)consists of a row of emitting optical fibers which tips are placed at asmall angle to the tips of receiving optical fibers, thus allowing thestimulating light to cross path with the stimulated light. This designhas the limitations mentioned earlier relating to the gap between theplate and the receiving optical fibers.

Unfortunately, in all these proposed designs, the confinement of thestimulating light to the imaging area is a great engineering challenge.All require precise alignment and registration to ensure that no areasof the plate, other than the imaging area, are exposed. It is thereforedesirable to provide techniques for reading images from storage-phosphorplates which maximize the efficiency with which image data are collectedwithout prohibitive expense.

SUMMARY OF THE INVENTION

According to the present invention, methods and apparatus are providedwhich not only overcome the problems described above, but actually usethe main technical obstacles in creating the various solutions describedherein. That is, according to various embodiments, instead of attemptingto compensate for or inhibit the lateral diffusion of stimulating lightin the turbid storage-phosphor medium, this laterally diffused light isactually used to effect indirect stimulation of an adjacent region ofthe storage-phosphor. The resultant release of stimulated light fromthat adjacent region is then captured by one or more detectors in directcontact (or close proximity) with surface of the storage-phosphor mediumabove the indirectly stimulated region.

By controlling the intensity of the stimulating light on one region of astorage-phosphor plate a well-defined diffusion distribution (andtherefore stimulation) under an adjacent region can be achieved.Efficient collection of the stimulated light released from thisindirectly stimulated region of the storage medium may then be effectedby one or more detectors in direct contact with (or at some very smalldistance from) the surface of the plate.

According to various specific embodiments, a light source, e.g., anarray of LEDs, is used to stimulate a region of the plate's surfaceadjacent a linear array of detectors. The array of detectors isconfigured to collect stimulated light from an adjacent region of theplate which results from the lateral diffusion of the stimulating lightinto the region under the array of detectors. The light source anddetector array are then scanned across the surface of the plate in onedimension to effect a line-by-line readout. According to a specificembodiment, the scanning of the light source across the plate alsoeffects a sufficiently complete erasure of the stored information.

More generally, the present invention provides methods and apparatus forretrieving information from a storage medium. A first portion of thesurface of the storage medium is exposed to stimulating light whichdiffuses in the storage medium under a second portion of the surfaceadjacent the first portion. The second portion of the surface isshielded from exposure to the stimulating light. Stimulated lightcorresponding to the information is received with at least one detectorpositioned to receive the stimulated light via the second portion of thesurface of the storage medium. The stimulated light is released from thestorage medium in response to the stimulating light diffused under thesecond portion of the surface.

According to one embodiment, an x-ray image capture device is providedwhich includes a storage-phosphor plate operable to capture incidentx-rays corresponding to an image. A stimulating light source is operableto expose a first portion of a surface of the storage-phosphor plate tostimulating light such that the stimulating light diffuses in thestorage-phosphor plate under a second portion of the surface adjacentthe first portion. The second portion of the surface is shielded fromexposure to the stimulating light. A linear array of detectors ispositioned to receive the stimulated light via the second portion of thesurface of the storage-phosphor plate, and convert the stimulated lightto electronic data corresponding to the image. The stimulated light isreleased from the storage-phosphor plate in response to the stimulatinglight diffused under the second portion of the surface. An actuatorassembly is operable to effect relative motion between the surface ofthe storage-phosphor plate and each of the stimulating light source andthe array of detectors in one dimension. According to a more specificembodiment, a cassette enclosure is provided having a form factorcorresponding to a standard radiographic film cassette, and having thestorage-phosphor plate, the stimulating light source, the array ofdetectors, and the actuator assembly enclosed therein.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram of a mechanism for reading informationfrom a turbid storage medium according to a specific embodiment of thepresent invention;

FIG. 2 is a simplified diagram of a mechanism for reading informationfrom a turbid storage medium according to another specific embodiment ofthe present invention;

FIG. 3 is a simplified diagram of a mechanism for reading informationfrom a turbid storage medium according to still another specificembodiment of the present invention;

FIG. 4 is a simplified diagram of a mechanism for reading informationfrom a turbid storage medium according to yet another specificembodiment of the present invention;

FIG. 5 is a simplified diagram of a line-scanning apparatus for use withvarious embodiments of the present invention;

FIG. 6 is a simplified diagram of a radiography cassette for use withvarious embodiments of the present invention;

FIGS. 7 a-7 c show the absorption profile of stimulating light and thepoint spread function of the resulting stimulated light for differentconcentrations of energy-absorbing dye in the plate according to variousembodiments of the invention;

FIG. 8 is a simplified diagram of a dual-layer phosphor plate designedaccording to and for use with specific embodiments of the presentinvention;

FIG. 9 is a simplified diagram of phosphor plate in a cassette housingillustrating a specific embodiment of the invention;

FIGS. 10 a-10 c illustrate three different approaches to providing aninterface between a storage plate and a photodetector array according tothe present invention;

FIGS. 11 a and 11 b show the architectures of a conventional linear CCDand a linear CCD designed according to a specific embodiment of thepresent invention, respectively;

FIGS. 12 a-12 c illustrate the pixel response of a conventional CCD(FIG. 12 a) and a CCD designed according to a specific embodiment of thepresent invention (FIGS. 12 b and 12 c);

FIG. 13 shows the architecture of an area CCD for use with a specificembodiment of the present invention;

FIGS. 14 a and 14 b respectively illustrate conventional clocking of a3-phase linear CCD and MPP burst clocking of a 3-phase linear CCDaccording to a specific embodiment of the present invention;

FIGS. 15 a and 15 b respectively show a conventional dual-stageamplifier for a linear CCD and a single-stage amplifier for a linear CCDaccording to a specific embodiment of the invention;

FIG. 16 is a simplified diagram of a bilinear CCD architecture accordingto a specific embodiment of the invention;

FIG. 17 is a simplified diagram of a linear CCD architecture accordingto a specific embodiment of the invention;

FIG. 18 is a simplified diagram of a linear CCD architecture accordingto another specific embodiment of the invention; and

FIGS. 19-24 illustrate radiography cassettes designed according tovarious specific embodiments of the invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

As discussed briefly above, specific embodiments of the presentinvention provide methods and apparatus for simply and efficientlyreading an x-ray image stored in a storage-phosphor plate using aphotodetector line array. More specific embodiments of the presentinvention provide methods and apparatus for reading a storage-phosphorplate in an enclosure of identical dimensions to those of a conventionalradiography film/screen cassette. Other embodiments and relatedapplications of the techniques of the present invention are describedbelow.

According to specific embodiments, the present invention providesmethods of light stimulating and collecting in storage-phosphor platereaders. Unlike other reading methods where the lateral diffusion of thestimulating light in the plate is a problem, specific embodiments of thepresent invention rely on such lateral diffusion to stimulate a lineararea of the plate which is in direct contact with a photodetector lineararray. The stimulating light impinges on an area of the plate adjacentto the area covered by the linear array. The stimulating lightpenetrates the phosphor and diffuses in all directions, includinglateral directions.

Since the phosphor layer is made of a white powder material, thestimulating light is not absorbed but reflected by the white granulesand propagates into turbid medium. The light propagation along thesurface of the plate is very short since some of the light is absorbedand most of the light is diffused back to the exposed area and towardsthe top and bottom of the plate. As will be described, some of thetechniques described herein allow for a self-aligned illumination whichis not only perfectly registered with the linear array, but alsowell-defined in terms of its width.

Whereas other methods require a very narrow illumination slit difficultto generate in a turbid material, some embodiments of the presentinvention rely on a knife-edge illumination which is easy to generateand which allows stimulation of a well defined and controlled regionbeyond the exposed area. The bleeding of stimulating light beyond theexposed area is in fact equivalent to a very narrow illumination slit.However, the width of the stimulating slit is not defined by complexcollimating optics, but rather by the attenuation coefficient of lightinherent in the phosphor material. It is therefore possible to generatethe equivalent of a very narrow illuminating slit which will stimulate alinear area of the phosphor material from within. According to variousembodiments, the fact that the stimulation area is not a narrow slitconfined within the collecting/imaging area (as described in otherpatents), but rather a wide rectangular area sharply defined on one sideonly by a photodetector linear array, also provides a solution toanother problem. As will be described, the additional exposure tostimulating light in some embodiments of the invention also provides forthe erasure of any residual information in the plate before it isreused.

That is, even though the stimulating light intensity and the scanningspeed are typically set so as to fully read out the plate underneath thelinear array, the bleaching process may not be 100% complete. Thus, theadditional exposure provided by the direct stimulating light is usefulto fully erase the plate before it is reused. This stimulation methodallows for the readout and erasing of the plate to occur simultaneouslywith a single scan. This is a significant improvement compared toconventional methods where the erasing of the plate occurs after thereadout has been completed, thus increasing the total cycle time of thesystem.

In most existing equipment, the plate is read out using a laser scanningmechanism and is then transported for exposure to a bank of incandescentor fluorescent high-power lamps for erasing. In addition to the obviousdisadvantage of these extra processing steps, such lamps use a lot ofpower, generate a lot of heat, and require a large enclosure. Accordingto further embodiments of the invention, if additional erasing of theplate is necessary or desired, the stimulating light source can beenergized while the array is scanned in the direction opposite to thereadout direction.

As mentioned above, the turbid nature of storage-phosphor media presentsa significant problem for previous techniques which relates toconfinement of the stimulating light to a precise area of the plate.That is, the stimulating light tends to diffuse laterally inside theturbid phosphor layer, thus undesirably increasing the area ofstimulation. This lateral diffusion effect, which is a problem inprevious designs, is actually a phenomenon on which the presentinvention relies for efficacy. According to a specific embodiment of theinvention and as shown in FIG. 1, the surface of a storage-phosphorplate 102 (comprising a storage-phosphor layer 104 on a plasticsubstrate 106) is exposed to stimulating light 108 (e.g., red light) ina region adjacent the imaging area (i.e., the area under photosensitivearea 112 of detector 114) rather than in the imaging area itself.According to various embodiments, stimulating light 108 may be deliveredin the form of a single LED or a laser pencil beam (e.g., for apixel-by-pixel readout), or an array of LEDs or a laser fan beam (e.g.,for a line-by-line readout). According to a specific embodiment, theregion directly exposed to stimulating light 108 and the imaging areaare adjacent linear regions on the surface of plate 102 and detector 114comprises a linear array of photodetectors.

According to specific embodiments and as shown in FIG. 1, the lineararray of photodetectors may be in contact or very close proximity withthe plate with the stimulating light source exposing the area of theplate adjacent to photodetectors. The linear array of photodetectors andthe stimulating light source are transported simultaneously across theplate with the linear array of photodetectors leading and thestimulating light source trailing. The area of the plate under thelinear array of photodetectors is read because of the diffusedstimulating light, and then, according to specific embodiments, is fullyerased by the trailing stimulating light.

The approach of the present invention runs counter to previoustechniques which generally try to avoid stimulating an area outside theimaging area for fear of not collecting all the stimulated light andlosing information. However, according to the invention, by stimulatingplate 102 in an area adjacent the imaging area, the imaging area becomesindirectly stimulated by light 116 laterally diffused within the platerather than by direct exposure to stimulating light 108. Thus, relianceon the lateral diffusion of stimulating light within the plate allowsstimulation of an area of the plate from the side rather than from thebottom or from the top. This, in turn, allows elimination (orminimization) of any gap between the plate and detector 114 which wouldotherwise be necessary for the stimulating light to impinge on the platein the same area as the imaging area. Indirect stimulation of a desiredregion of the plate in this manner allows for the detector(s) to beplaced in direct contact with (or in very close proximity to) theimaging region, thus resulting in high collection efficiency as well ashigh spatial resolution.

Unlike a previously mentioned design where a strip of a plate isstimulated from one side of the plate and imaged from the other, thisdesign does not require a special transparent plate. Rather, it can beimplemented using conventional turbid storage-phosphor plates. This is asignificant benefit in that transparent plates are expensive and verydifficult to manufacture whereas conventional plates are easy tomanufacture and readily available. Another benefit of the design of thepresent invention is that the stimulating hardware and collectinghardware may be disposed on the same side of the plate. According tosuch embodiments, the overall profile of the hardware can be made verylow. According to one such embodiment (described below), the hardware isconfigured so as to fit into an enclosure with dimensions substantiallysimilar to those of a standard film cassette. As will be understood,such an embodiment would be problematic (and likely impracticable) usingstimulating hardware and collecting hardware on opposite sides of theplate.

Yet another benefit associated with placement of the stimulatinghardware and collecting hardware on the same side of thestorage-phosphor plate relates to the alignment and registration of thestimulating hardware with the collecting hardware. According to aspecific embodiment which will be described with reference to FIG. 2, aself-aligned assembly of the stimulating and collecting hardware isprovided.

FIG. 2 shows a self-aligned arrangement for the stimulating light. Thatis, the linear array of photodetectors blocks the stimulating light fromthe plate. The edge of the linear array defines the boundary between thearea of the plate directly exposed to the stimulating light and the areaof the plate indirectly exposed to stimulating light through diffusion.More specifically, a linear array 202 has a photosensitive area 204which extends to the edge of its substrate. The area of plate 206adjacent that edge is exposed to stimulating light 208 to achieve aperfectly aligned and well-controlled stimulation area under lineararray 202. That is, even though the width of stimulating light 208 isnot confined to the area to the left of linear array 202, linear array202 acts as a knife edge for stimulating light 208, forming aself-aligned mask which allows surface exposure only to a linear regionadjacent photosensitive area 204 of array 202.

The width of the stimulated area under photosensitive area 204 relatesto the intensity of stimulating light 208 in the exposed region of theplate as well as the attenuation coefficient in the plate itself. Forexample, in some media the intensity of the laterally diffusedstimulating light decreases exponentially moving away from the edge ofan exposed region in a well defined manner. Thus, depending on thecharacteristics of specific media and the desired resolution, thestimulating light intensity and/or the linear array photosite may bevaried in accordance with particular applications of the presentinvention. A significant advantage associated with the self-alignednature of such an embodiment of the invention is the fact that carefulfocusing of the stimulating light using, for example, a laser fan beam,is not necessary. In fact, the applied light can be relatively diffuseas delivered, for example, with an inexpensive array of LEDs.

FIGS. 1 and 2 illustrate some of the basic principles of the presentinvention. However, it will be understood that in some cases it will notbe practical to position a linear array of photodetectors in contactwith a phosphor plate. That is, the photosensitive side of the lineararray often includes the bonding area for the interconnecting wires.These wires typically protrude above the photosensitive surface andprevent any other surface from being placed against it. These wires arealso very small and fragile and must be protected from any directcontact with a moving surface. The photosensitive surface of the lineararray itself is also fragile and needs to be protected from directcontact with a moving surface. One method for protecting both the wirebonds and the photosensitive surface involves the use of a fiber-opticfaceplate between the photosensitive surface of the linear array and thephosphor plate. In such an implementation, the fiber-optic faceplate maybe permanently bonded to the photosensitive side of the linear array,thus clearing the wire bonds from the phosphor plate. FIG. 3 illustratessuch an specific embodiment in which collection of stimulated light inresponse to laterally diffused stimulating light is effected through afiber-optic face plate 302. It should be noted that the gap between thesurface of storage medium 304 and fiber-optic face plate 302 has beenexaggerated for illustrative purposes.

FIG. 4 shows a further refinement of the arrangement shown in FIG. 3. InFIG. 3, the edge of the fiber-optic faceplate creates the boundarybetween the directly exposed area of the plate and the indirectlyexposed area of the plate. The sharpness of this edge is important tothe uniformity of the diffused light profile under the detector array.By placing two fiber-optic faceplates against each other (one forillumination with stimulating light, one for collection of stimulatedlight) it is possible to protect the edge of the collecting faceplateagainst chipping and cracking of the edge of the collecting faceplate.According to this embodiment, a single apparatus is provided to effectboth the stimulating and collecting functions. As will be understood,this configuration facilitates simultaneous scanning of the stimulatingand collecting apparatus as well as provides a low profile for packagingof the readout apparatus with the storage medium in, for example, astandard radiography cassette.

In the embodiment shown, the linear array of detectors 404 are combinedin ceramic package 406 with a two dimensional array of LEDs 408 whichprovide the stimulating light to storage-phosphor plate 410 whichcomprises a storage phosphor layer 412 on a plastic substrate 414. Thestimulating light from LEDs 408 is transmitted to the surface of thephosphor 412 via a first fiber-optic faceplate 416. Alternatively,faceplate 416 may comprise a block of uniform material such as glass orplastic as transmission of the stimulating light to the surface ofphosphor 412 via fibers is not critical to the operation of theinvention.

As described above with reference to various other embodiments of theinvention, the stimulating light diffuses in phosphor 412 into theregion below the photosensitive regions 418 of detectors 404. Thisindirect stimulation of this region of phosphor 412 results in therelease of previously stored information as stimulated light which isthen captured by detectors 404 via a second fiber-optic faceplate 420.

Not shown in the figures to which the foregoing description refers issome means for inhibiting or absorbing the stimulating light diffusedback by the plate towards the linear array of photodetectors. As withconventional laser scanning methods, such filtering is important toproper system operation. That is, since the stimulated light is muchdimmer than the stimulating light and is the only light containing imageinformation, it is important to prevent stimulating light from reachingthe photodetectors. Various techniques for blocking the stimulatinglight will be described below.

Referring back to FIG. 4, because the source of the stimulating lightand the means by which the subsequently released energy is captured aredisposed in the same package, alignment of these two elements isconsistent and reliable. In addition, the simultaneous and coordinatedscanning of the arrays of LEDs and detectors across the surface of thestorage-phosphor plate (as illustrated in FIG. 5) can be managed with asingle mechanism such as, for example, a precision stepper motor.

FIG. 5 shows a system 500 for capturing and reading out image data foruse with, for example, radiography systems. Once an image is captured instorage medium 502 (e.g., a storage-phosphor plate), the release andcapture of the stored information may be effected by scanning a linearreadout apparatus 504 designed according to the present invention acrossthe surface of storage medium 502. According to various embodiments,readout apparatus may comprise a single apparatus such as that describedabove with reference to FIG. 4 in which both the source of stimulatinglight and the detector array are included. Alternatively, apparatus 504may comprise two separate apparatus the operation and scanning of whichare closely coordinated to effect readout in the manner describedherein.

That is, regardless of the specific mechanical nature of apparatus 504,readout of information in storage medium 502 is effected by indirectstimulation of the region of interest according to the techniquesdescribed above. Movement of apparatus 504 may be controlled viascanning control 506 which generates signals to control a mechanicalactuator 508 which may include, for example, a precision stepper motor.As will be understood, any of a variety of techniques may be employed toeffect the precise, e.g., line-by-line, scanning of readout apparatus504 over storage medium 502.

Stimulated light is released from storage medium 502 and captured by thedetectors of readout apparatus 504 as controlled by readout control 510according to any of a variety of well know techniques which convertcaptured radiation to electrical or optical data which may then bestored for later retrieval. It will be understood that scanning controland readout control via 506 and 510 may effected in a variety of wayswithout departing from the scope of the present invention. For example,such control may be effected using microprocessor controlled circuitry,application specific integrated circuits, or software.

FIG. 6 illustrates yet another specific embodiment of the presentinvention in which a readout apparatus and storage medium combinationsuch as that described above with reference to FIG. 5 may be integratedin a cassette 602 which may be a standard size for a particularapplication, e.g., a radiography cassette. Control of the readoutmechanism 604 and readout of data from storage medium 605 could beeffected via connector (not shown) which may comprise any of a varietyof commercially available parallel or serial connectors. Alternatively,readout of data could be effected via one or more conductors exitingcassette 602.

In the radiography context, such a device could be conveniently usedwith the existing installed base of radiography systems. That is, thestandard size cassettes could be inserted into an existing radiographytable for capture of x-ray images in the same manner as the standardfilm cassettes. The image data may then be read through suitableconnections, e.g., a connector or bundle of conductors, while thecassette conveniently remains installed in the radiography table, i.e.,in-situ readout. Alternatively, the cassette may be removed andconnected to a reader (which may be a conventional PC or work station).Readout (and simultaneous erasure) of the stored information is theneffected in the manner described above, after which the cassette isready for subsequent image capture.

According to various embodiments, the present invention includesimplementations integrated into any standard size radiography cassettesas defined by international standard IEC 60406, the entire disclosure ofwhich is incorporated herein by reference for all purposes. Specificexamples of cassette dimensions include, but are not limited to,14″×17″, 14″×14″, 10″×12″, 8″×10″, 35 cm×43 cm, 35 cm×35 cm, 20 cm×40cm, 18 cm×43 cm, 13 cm×18 cm, 13 cm×30 cm, 18 cm×24 cm, and 24 cm×30 cm.

Given the state of the art of the capture and processing of image data,a line-by-line scanning of a standard 14″×17″ image could be effectedusing the techniques of the present invention in roughly 10 secondswhich compares favorably to the several minutes required for developmentof conventional film. In addition, the image is electronically storedand can be permanently archived for later retrieval without having tophysically store the large developed image.

It should be noted that nature of the apparatus integrated in a cassettesuch as cassette 602 may vary without departing from the scope of thepresent invention. For example and as described above, the readoutapparatus and mechanical scanning mechanism can take a variety of forms.In addition, various parts of the scanning and readout control may beintegrated with cassette 602. For example, one or more microprocessorsand associated control circuitry may be included in cassette 602 toeffect scanning and image capture as instructed by control signals froman external computer. Scanning and image capture could even be effectedentirely within the cassette which could include sufficient onboardmemory for temporarily storing the image until it can be downloaded forviewing and archiving.

Alternatively, generation of control signals for scanning and imagecapture may be effected entirely outside of the cassette with data beingtransmitted back and forth via, for example, a connector. In any event,the present invention contemplates and encompasses any of a variety ofcombinations of on and off board control of the scanning and datacapture functions.

As should be well understood at this point, the fundamental principle ofthe present invention is the stimulation of an area of a storage platethrough lateral diffusion of the stimulating light within the plate. Toimprove the performance of systems based on this fundamental principle,a number of optimizations may be made for each of the components of sucha system. As will become clear, some of these optimizations areindependent of this fundamental principle, and as such constituteindependent inventions. Various components of such systems are discussedherein and include storage plates, fiber-optic faceplates, sources ofstimulating light, linear arrays of photodetectors, filters for blockingstimulating light, scanning mechanisms and system housings.

Storage Plates

Since the methods of stimulation and collection described herein aredifferent than conventional laser scanning techniques, the physicalparameters of the storage plate employed for the present invention maybe correspondingly different. That is, the thickness of the plate, thegrain size of the phosphor, the amount of binder, and the amount of dyemay be altered from that which is appropriate for conventionaltechniques for improved performance of the techniques of the presentinvention.

Exceeding a certain level of concentration of energy-absorbing dye inplates read by conventional laser scanning techniques can be problematicsince high concentrations of such dye would tend to prevent the entirethickness of the plate from being stimulated. By contrast, according tothe various techniques of the present invention, plates with very highconcentrations of energy-absorbing dye may be employed to achieveparticular absorption and stimulation characteristics because theintensity of the stimulating light may simply be increasedcorrespondingly without the negative effects suffered by conventionaltechniques.

For example, the amount of energy-absorbing dye (i.e., dye which absorbselectromagnetic energy at the wavelength of the stimulating light, e.g.,red light) in the storage plate can be manipulated to control the amountand profile of the lateral diffusion of the stimulating light as shownin FIGS. 7 a-7 c. Each pair of graphs in FIGS. 7 a-7 c shows theabsorption profile of the red stimulating light (top graph) and thepoint spread function of the resulting blue stimulated light (bottomgraph) for different concentrations of red-absorbing dye in the plate assimulated using the Monte Carlo simulation technique. Each gradation inthe respective graphs represents a 10% increment.

The graphs of FIGS. 7 a-7 c indicate that it is now possible, with thetechniques described herein, to indirectly stimulate the plate with thesame energy level across its entire depth. These graphs illustrate thefact that, as the stimulating light diffuses further and further awayfrom the exposed edge, its energy distribution becomes homogeneousacross the entire thickness of the plate. This phenomenon can be used tocreate an x-ray imaging system with very high resolution and yet verygood x-ray absorption.

Since very bright illumination can be easily achievable (multiple rowsof high-power red LEDs), it is possible to reach full bleaching of theplate at only 10% of the direct stimulating light intensity. With a highamount of red-absorbing die, the plate can be read out through itsentire depth across a very narrow strip. This configuration isparticularly useful for mammography imaging, which requires highresolution as well as high x-ray absorption (i.e., high DQE). It istherefore theoretically possible to achieve higher resolution across themechanical scanning direction than across the direction of the linearCCD.

In the direction of the linear CCD, the resolution is limited by thelateral diffusion of the stimulating light as well as the stimulatedlight. In the direction of the mechanical scanning, the resolution isonly limited by the lateral diffusion of the stimulating light (whichcan be controlled by the amount of red-absorbing dye) and not by thelateral diffusion of the stimulated light. The photodetectors aperture(along the direction of the mechanical scanning) does not impact theresolution but simply the collection efficiency. Even with a 200 μmphotodetector aperture, it is possible to achieve much finer resolution(as low as 20 μm).

Using a Monte Carlo computer simulation, one can optimize the phosphorgrain size, the red-absorbing dye concentration and the plate thicknessto achieve maximum performance for a particular application. This methodoffers great potential for achieving very high resolution and high x-rayabsorption without relying on needle phosphor technology. Currentproducts used for mammography and other high-resolution x-ray imagingutilize dentritic phosphor layers (needles of Cesium iodide CsI) tochannel the emitted light across the thickness of the plate. Thesephosphor layers are very expensive and difficult to manufacture. Inaddition, they are very hygroscopic and exhibit objectionable imageburn-in (i.e., areas of the needle phosphor strongly exposed to x-raysexhibit higher luminous gain than surrounding areas).

Using the method of stimulation and collection described herein, theresolution of a turbid storage-phosphor plate in the direction ofmechanical scanning can be as high as the resolution of a needlephosphor plate. This is true even when a thick storage-phosphor plate(i.e. 300 μm) is used to capture high energy x-rays.

In another embodiment shown in FIG. 8, two layers of storage-phosphormaterial are deposited on the same substrate 802. The top layer 804contains a small amount of dye which is meant to absorb weakly thestimulating light, the bottom layer 806 contains a higher amount of dyewhich is meant to absorb strongly the stimulating light. When scannedwith a bilinear photodetector array 808 using the method describedherein, the top layer 804 is stimulated further away from the edge ofthe direct stimulating light exposure than the bottom layer 806.According to a more specific embodiment, stimulated light from the toplayer is collected in the first row of photodetectors 810 whereasstimulated light from the bottom layer is collected in the second row ofphotodetectors 812.

In addition and because of the x-ray absorption characteristics of thestorage-phosphor material, the top layer 804 absorbs low energy x-rayswhereas the bottom layer 806 absorbs higher energy x-rays. Similarly,soft material (such as human soft tissue) absorbs preferentially lowenergy x-rays whereas dense material (such as human bone) absorbspreferentially high-energy x-rays. Therefore, according to anotherspecific embodiment of the invention, information collected from the topand bottom layers is used to create a dual-energy image. Dual energydata may then be processed to extract information corresponding to boneor soft tissue only. In addition, images may be created which displaybones only or soft tissue only. In general, a variety of embodiments areenvisioned using multiple layers of various storage-phosphor materialsand multiple rows of photodetectors to achieve dual-energy imaging.

Traditionally, phosphor plates are manufactured on a flexible substrate(PET, Mylar) like prompt phosphor screens. These plates are eithermounted on a hard backing (e.g., an aluminum plate) or are kept flexiblein order to be transported and read in the laser scanning apparatus.Therefore, according to a specific embodiment of the present invention,in order to maintain sufficient contact between the surface of such aflexible phosphor plate and the light collection apparatus, e.g., afiber-optic face plate, the phosphor plate is mounted on a thin foamlayer which is compressed when the light collection apparatus is pressedagainst the surface of the plate. According to a more specificembodiment, where the light collection apparatus is held at each side,the foam can be make thicker at the center of the plate than at the edgeto ensure sufficient contact across the entire width of the plate (e.g.,see FIG. 9).

The fiber-optic faceplate According to various embodiments, thefiber-optic faceplate of the present invention (e.g., plates 302 and 420of FIGS. 3 and 4) may serve two purposes, i.e., creation of a knife-edgealignment for the stimulating light, and collection of the stimulatedlight onto the photo detectors. As mentioned above, the edge of thefaceplate defines the illumination boundary and its sharpness isimportant for achieving optimal performance. To protect the physicalintegrity of the edge of the fiber-optic faceplate, another suchfaceplate can be mounted against it (e.g., plate 416 of FIG. 4) or,alternatively, a clear block of transparent material (e.g., glass orplastic) can be mounted against it. The choice of material will dependon the amount of collimation required for the stimulating light. If noadditional collimation is required, a clear material can be used. Ifadditional collimation is required, another fiber-optic faceplate can beused to transport the stimulating light onto the plate. As will beunderstood, the amount of additional collimation is determined by thenumerical aperture of the fiber-optic faceplate. If a low numericalaperture is chosen, the stimulating light hitting the plate will behighly collimated. Regardless of the nature of the block mounted againstthe collection face plate, the edge of the collection faceplate isprotected against chipping or other damage during operation.

According to a specific embodiment and to facilitate its mounting ontothe linear array of photodetectors, the fiber-optic faceplate may be cutat a slight angle with respect to the direction of the fibers as shownin FIG. 4. Such a slight bias cut may allow for an easier alignment ofthe faceplate onto the linear array without reducing significantly itstransmission characteristics, e.g., a bias cut angle of less than 10degrees will result in a 10% transmission reduction.

According to other specific embodiments of the invention, the collectionfiber-optic faceplate may also serve another important purpose. That is,it can be configured to block partially or completely the stimulatinglight. In order to provide such blocking, the fiber-optic faceplate maybe constructed from materials which absorb the stimulating light andtransmit the stimulated light. Such materials may include optical filtermaterials such as ionically colored glass e.g. Schott BG3. However, thedifficulties associated with drawing such materials into fibers andbundling them into fiber-optic faceplates (e.g., such glasses have a lowrefractive index and are not stable through various heat treatments) maynot make them the best materials for such an implementation.

Other materials such as rare earth doped filter glasses are bettercandidates for fiber-optic faceplates. Developed originally for theirfluorescence properties, rare earth doped filter glasses may also beused as a filter material. In particular, Thulium doped glass has goodtransmission characteristics at 400 nm and good absorptioncharacteristics at 680 nm. Therefore, according to a specific embodimentof the invention, a low index host glass and a high index host glass aredoped with Thulium to create a cladding and a core material. These coreand cladding materials are then bundled together to create fiber-opticfaceplates for use with the present invention having good transmissioncharacteristics (i.e., high numerical aperture) and good rejection ofstimulating light.

As is well known, the transmission of a fiber-optic faceplate is afunction of the numeral aperture of each fiber. The numerical apertureof each fiber increases as the difference in refractive indexes betweenthe core and cladding increases. Fiber optic faceplates aretraditionally manufactured from glass since high index and low indexmaterials are easily available. This has not been the case for plasticmaterials, i.e., most of them tend to have a refractive index close to1.4. A new plastic material is now commercially available from theFlorida-based company Optical Polymer Research Inc. Until recently, mostfiber-optic faceplates have been manufactured from glass since materialshaving a sufficient index differential are easily available. Recently, anew class of plastic material has been developed. This new material,marketed under the name Opti-Clad, has a very low refractive index (lessthan 1.36) and as such is suitable for use as a cladding materialaround, for example, a styrene core (refractive index close to 1.59).Teflon is also another good cladding material since its refractive indexis 1.3. As a result of this advance in materials science, it is nowpossible to manufacture plastic fiber-optic faceplates with highnumerical apertures. According to a specific embodiment of the presentinvention, an energy-absorbing dye is introduced into the plasticemployed to make such a fiber-optic faceplate to obtain a faceplate witha high numerical aperture and good rejection of stimulating light.

Another approach to blocking the stimulating light involves the use of areflective (rather than refractive) cladding material in the fibers ofthe fiber-optic faceplate. Such fibers are not ideal for transmission oflight energy over long distances due to the loss of energy at eachreflection. However, given the short distance contemplated in mostimplementations of the present invention (e.g., less than 1″), suchfibers will be sufficiently transmissive.

As discussed above and according to various embodiments, the fiber opticfaceplate may be useful for creating a knife-edge for the stimulatinglight, for collecting and imaging the stimulated light onto thephotodetectors, and additionally for preventing the stimulating lightfrom reaching the photodetectors. It is possible however to implementthe present invention without using a fiber optic faceplate (as shown inFIGS. 1 and 2).

It is also possible to use a plain transparent layer (glass or plasticmaterial) between the image plate and the photodetectors so as toprevent the bonding wires from touching the image plate. If noprecautions were taken, such a transparent layer would introduce anunacceptable amount of blurring due to the fact that the image plate isa Lambertian emitter and the stimulated light would diffused in alldirections in the transparent layer before reaching the photodetectors.On one hand, the thickness of the transparent layer must be kept to aminimum to prevent blurring; on the other hand the layer must be thickenough to provide the necessary clearance between the plate and thephotodetectors for the bond wires. According to specific embodiments ofthe present invention, a number of techniques can be used independentlyor in conjunction in order to reach the correct compromise.

According to a first such technique, a beveled transparent layer isemployed which is thin above the photosensitive area of the linear arrayand thick above the bonding area of the linear array. This implies thatthe linear array is not positioned parallel to the image plate. As shownin FIG. 10 b, the linear array 1002 is placed at an angle with respectto the plate 1004 so as to bring the photosensitive area 1006 closer tothe plate and the bonding area further away from the plate. Using thistechnique, one can minimize the thickness of the transparent layer 1008over the photosensitive area and maximize it over the bonding area.

According to a more specific embodiment, the linear array is placed in acavity and a liquid transparent epoxy is poured over it. Once the epoxyhas cured, it creates a hard transparent layer which is thin over thephotosensitive area and thick over the bonding area of the linear array.The bond wires can be directly encapsulated by the epoxy or can be firstcoated with a resilient material (e.g., silicone) before they arecovered with the epoxy so as to alleviate issues related to mismatch incoefficients of thermal expansion. In order to guarantee that thesurface of the epoxy in contact with the plate will be perfectly flat,it is proposed to create a mold in which the proxy will be poured. Forexample, the mold can be as simple as a perfectly flat Teflon-coatedsurface placed in front of the linear array which will hold the epoxywhile it is poured and which will be removed after the epoxy has cured.According to one embodiment, a one-part epoxy such as 4021T manufacturedby Ablestick is employed. This epoxy will adhere to glass and siliconbut will not stick to the Teflon-coated surface. The transparent epoxycan also contain the absorbing dye necessary to block out thestimulating light (as it is described further on in this document).

A second technique illustrated in FIG. 10 a comprises using atransparent layer 1022 made of a high index material (n˜1.6). Lightemitted from the plate 1024 will be refracted in the high index material1022 at a smaller angle with respect to the normal incidence (Snelllaw). The resulting blurring will thus be reduced.

A third technique illustrated in FIG. 10 c comprises depositing aninterference filter 1042 on the surface of the transparent layer 1044 incontact with the image plate 1046. The purpose of the interferencefilter is to transmit the stimulated light emitted by the plate thatreaches the filter at angles close to normal incidence, and to reflectback to the plate the stimulated light that reaches the filter beyond acertain angle. This type of interference filter is used in front ofprompt-emitting phosphors in order to create a forward-peakingdistribution, that is to increase the intensity of the light emission inthe forward direction and to decrease it in the off-axis directions.This technique is particularly useful for maximizing the opticalcoupling between a CRT phosphor screen and a projection lens (e.g., in alarge-screen TV), or between a prompt emitting phosphor and a lens-basedcamera (Norikata Satoh, SPIE volume 2432 page 462-469). This techniqueincreases the intensity of the light emitted in the forward direction atthe expense of the spatial resolution. This technique is used in thisinvention not for the purpose of collecting more light but for thepurpose of rejecting off-axis light that contributes greatly to theblurring effect.

Regardless of which material is used over the linear array (e.g., fiberoptic faceplate, glass, plastic or epoxy layer), this material shouldnot scratch the image plate. Removing dust and dirt from the contactarea will reduce chances of scratches. In a specific embodiment, anadditional layer of Teflon-like material is coated on the plate or thematerial itself to reduce friction between the two surfaces. In anotherspecific embodiment, the outer edges of the surface in contact with theimage plate are beveled or rounded to reduce the chances of scratches.

The Source of Stimulating Light

Various embodiments of the present invention have been described hereinin which the source of stimulating light comprises a row of lightemitting diodes (LEDs) mounted close each other. Such arrays of LEDs areavailable commercially, e.g., StockerYale linelights. Examples of suchmodules include 100 LED chips mounted directly on 100 mm substrate witha spacing between each LED of 1 mm. The overall illumination of atypical LED array is fairly uniform across the length of the array. Oneof the advantages of the method of light stimulation proposed in thepresent invention is that it can be made relatively insensitive tovariations of illumination across the length of the array by ensuringthat the amount of illumination is sufficiently high to bleach theentire depth of the plate. According to one embodiment, reaching thisthreshold is ensured by including one or more additional rows of LEDsnext to the first row in order to increase the amount of stimulatinglight in the plate.

According to a specific embodiment, the LEDs' peak emission wavelengthmatches the peak absorption wavelength of the filter which is placedbetween the plate and the photodetectors. In addition, the LEDs arechosen to have an emission spectrum range which is narrower than theeffective absorption range of the filter. In one embodiment where thisis not the case, an additional filter is added between the LEDs and theplate. The purpose of this additional filter is to block any wavelengthof stimulating light which would not be blocked by the primary filterbetween the plate and the photodetectors. In another specificembodiment, control circuitry is provided to adjust the brightness ofthe LEDs. The control circuitry can be used to reduce the brightness ofthe LEDs in order to achieve partial bleaching of the plate.

In yet another specific embodiment, additional rows of different colorLEDs are provided to achieve greater erasing efficiency. It has beendemonstrated that storage-phosphor plates are more efficiently erasedunder broadband illumination than monochromatic illumination. Therefore,adding rows of ultra-violet, blue, green, yellow, orange or infraredLEDs to the rows of red LEDs is proposed to simulate broadbandillumination and increase the erasing efficiency.

It has also been demonstrated that some storage-phosphor plates are moreefficiently erased using a two-stage erasure method. Such a two-stageerasure method is described in Fuji Computer Radiography TechnicalReview No. 2 (New Technological Developments in the FRC 9000) on page18. It consists of exposing the plate to ultra-violet light in a firststage, and to broadband illumination without ultra-violet light in asecond stage. Fuji implements this method by passing the plate over astack of high brightness fluorescent light tubes, where some of them aredirectly exposed to the plate and some are covered with a UV cut-offfilter.

A specific embodiment of the present invention introduces a novel way toimplement a two-stage erasure method. Fluorescent tubes are replacedwith rows of LEDs. A first erasure stage is constructed using UV LEDsonly. UV LEDs are now commercially available from a number ofmanufacturers (e.g. Nichia NSHU-550E or NSHU-590E). These LEDs put outapproximately 1 mW between 370 nm and 375 nm. They also produce a verylow visible output (dim purple glow) which can be easily filtered out. Asecond erasure stage is constructed using various other color LEDs whichdid not produce any UV light.

The Linear Array of Photodetectors The linear array of photodetectorsfor use with the present invention (e.g., arrays 114, 202, and 404described above) can be built in a variety of different ways. Forexample, discrete photodetectors can be mounted in a single row andconnected to a multiplexing circuitry. Alternatively, an amorphoussilicon array of photodetectors can be used. In order to achieve alow-noise readout, photodetectors built on a single crystal siliconsubstrate are preferred. Such linear arrays can be manufactured usingcharge-coupled device (CCD) or CMOS technology. CMOS technology forimage sensors has improved tremendously in the last few years and theperformance characteristics of CMOS image sensors are approaching thoseof CCDs. It should be understood that the present invention does notexclude any of the available photodetection technologies. With regard tothe performance of linear CCDs, various embodiments of the presentinvention provide further enhancements which will now be described.

Conventional linear CCDs rely on photodiodes or junction gates as aphotodetectors. Both designs provide photodetectors with high quantumefficiency (˜60%) in the blue region of the spectrum because they arenot covered by the polysilicon gates used in the register (which absorbstrongly in the blue). The intrinsic quantum efficiency of today'slinear CCDs is close to the theoretical limit. However, the extrinsicquantum efficiency is lower due to the large amount of light reflectedoff the silicon surface. This, in turn, is due to the fact that therefractive index of silicon is high. Successful attempts have been madeto improve the quantum efficiency of back-illuminated area CCDs throughthe use of anti-reflective coatings. However, no product nor literaturehas reported any similar efforts to improve the quantum efficiency ofconventional front-illuminated linear CCDs. Therefore, the presentinvention provides antireflection coatings for linear CCD arrays toreduce the amount of reflection off the silicon surface. Multi-layercoatings (e.g., Haffnium oxide) can be used to increase the quantumefficiency of front-illuminated linear CCDs from 60% to 95% at 400 nm(e.g., the wavelength of stimulated light). In addition, suchmulti-layer coatings can also be used to decrease the quantum efficiencyof front-illuminated linear CCDs from 80% to 1% by reflecting light at650 nm (e.g., the wavelength of stimulating light). That is, thesemulti-layer coatings can be implemented to act as a blocking filter forthe stimulating light and an antireflective layer for the stimulatedlight.

As discussed previously, conventional linear CCDs rely on photodiodes orjunction gates as a photodetectors. In order to create such photodiodesor a junction gate photodetectors, additional process steps are takenwhich increase the cost and complexity of the CCD manufacturing process.An easier and cheaper process could be used to manufacture linear CCDs,such as the one used for full-frame area CCDs, but it would be at theexpense of the blue quantum efficiency. Full-frame area CCDs use asimple manufacturing process in which the vertical registers act asphotodetectors. They exhibit a low quantum efficiency in the blue regionof the spectrum (˜10%) because the vertical registers are covered withpolysilicon gates which absorb strongly at these wavelengths. Attemptshave been made to increase the blue quantum efficiency by thinning thepolysilicon gates or removing such gates over parts of the photodetectorarea.

Therefore, according to a specific embodiment of the invention, atechnique is introduced to increase the blue quantum efficiency oflinear CCDs manufactured using a conventional full-frame area CCDprocess. The proposed photodetector layout includes a narrow polysilicongate (i.e., a photogate) surrounded on both sides by wide channel stopregions (which are not covered by polysilicon gates). This photodetectordesign is dramatically different from conventional linear CCDphotodetectors since the channel stop region between the photodetectorsis much wider than the photodetector itself (see the comparison in FIGS.11 a and 11 b).

Traditionally, narrow channel stop regions 1102 are implanted betweenphotodetectors 1104 to form a sharp potential barrier between them (FIG.11 a). The channel stop region exhibits high quantum efficiency but nostrong electric field, so electrons generated in that region canlaterally diffuse on either sides to the two adjacent photodetectors. Inmost linear CCD designs, the channel stop width is kept to a minimum tocreate the sharpest separation possible between photodetectors, thusincreasing the contrast (i.e., MTF). The photodetector response can berepresented by a trapezoid-shaped curve, which approaches the shape of arectangle if the channel stops are narrow compared to the photodetectorwidth (FIG. 12 a).

By contrast and according to a specific embodiment of the invention,channel stops 1152 are wider than the photodetectors 1154 (FIG. 11 b),which creates a triangular-shaped photodetector response curve (FIG. 12b). As can be seen from the figure, this reduces the isolation betweenadjacent photodetectors (i.e., creates a more overlapping response).According to a more specific embodiments, this effect is mitigated byproviding photodetectors on a finer pitch than the required resolutionand combining their signals at the output of the CCD register (analogbinning technique) or after they have been digitized (FIG. 12 c). Thisdesign achieves the original goal of increasing the blue quantumefficiency and also helps decrease the dark current generation in thephotodetector since channel stop regions generate less dark current thanCCD channels.

According to another embodiment, an area CCD is used to emulate a linearCCD, i.e., signals from the photodetectors of the same column of an areaCCD are combined in the horizontal output register to form a singlelarge-aperture photodetector. For example, five 44 μm×44 μmphotodetectors may be binned to emulate a 220 μm×44 μm photodetector.The proposed area CCD resembles a Time Delay Integration (TDI) CCD inits aspect ratio (5×2,048 pixels), but it is not used in a TDI mode.This design alleviates the serious problem of readout lag encounteredwith large-aperture photodetectors.

That is, photodetectors with an aperture greater than 100 μm exhibitsignificant readout lag as reported in the data sheets of linear CCDsdesigned for barcode readers (e.g., Toshiba TCD1304AP, Sony ILX511).This is due to the fact that the electric field in the photodetectorregion is not strong enough to move small charge packets across a 100 μmdistance into the output register. In the case where an area CCD is usedinstead of a conventional linear CCD, the gate length can be kept under15 μm. Since no spatial resolution is required along the columns of thearea CCD, larger gates can be used with no implant barriers betweenthem. An example of such a design is illustrated in FIG. 13. Five 44 μmphotogates 1302 are laid out vertically along the CCD buried channel. Asshown in the associated timing diagram, the photogates are biasednegatively during the integration time (MPP mode described below) andclocked briefly in a ripple fashion to transfer the charge packets intothe output register.

In this mode of operation, the device is truly a linear CCD since itcannot image in the vertical direction. Even though the device layoutresembles one of an area CCD, the photogates can only ripple the chargeinto the output register but cannot isolate separate charge packetssince they are all tied to the same voltage. As described in a previousembodiment (dual-layer plate for dual-energy imaging), it may benecessary to collect information from two adjacent rows ofphotodetectors instead of one. It is possible to operate the same lineardevice shown in FIG. 8 as a bilinear device (two adjacent rows ofphotodetectors) by simply changing the photogates timing. If V_(PG3) ispinned to the substrate while the other four photogates are dithered,V_(PG3) acts as a barrier between a first photodetector (consisting ofV_(PG1) and V_(PG2)) and a second photodetector (consisting of V_(PG4)and V_(PG5)). The fact that four photogates are dithered during theintegration time (instead of being pinned to the substrate) does notadversely effect the dark current performance (see MPP operation detailsbelow) provided that the dithering of the photogates is fast enough.

At room temperature, conventional linear CCDs generate enough darkcurrent to significantly degrade the image quality required for thisapplication. A solution to this problem is to cool the CCD, which is nota simple task because of condensation issues. To avoid the requirementof cooling the device, a specific embodiment of the present inventionprovides a method for reducing the dark signal of the linear CCD. Thismethod is inspired from the technology known as MPP, which was developedfor areas CCDs only. The MPP technology significantly reduces the darkcurrent generated in the vertical registers of area CCDs. This isaccomplished by introducing a weak implant under one gate and by biasingall the gates negatively (total inversion) to pin the Si—SiO₂ interfaceto the substrate voltage (MPP: Multi-Pinned Phase). Further details canbe found in the book entitled “Solid-state imaging with charge-coupleddevices”, A. Theuwissen, on page 289.

This technology has been previously implemented in the verticalregisters of area CCDs but not in the horizontal output registers ofarea CCDs nor in the output registers of linear CCDs. The reason is thatthe MPP mode only reduces dark current generation when the gates arepinned to a negative voltage, and not when the gates are clocked to apositive voltage. In the operation of an area CCD, the gates of thevertical registers are most of the time pinned to a negative voltage(during the read out of the horizontal output register) and only clockedto a positive voltage during a short period of time (i.e., very low dutycycle). Under such conditions, the MPP mode is very effective. However,timing diagrams are quite different for output registers of area CCDsand linear CCDs. That is, the gates of such devices are usually clockedconstantly and do not get pinned to a low voltage for any significantlength of time (i.e., the high duty cycle of FIG. 14 a). Under thoseconditions, the MPP operation would not be effective at all and this iswhy it has not been implemented on any commercial devices.

According to a specific embodiment of the invention, the MPP mode isimplemented in the output register of a CCD by introducing an MPPbarrier implant under one gate and by clocking all the gates in a burstmode instead of a continuous mode (FIG. 14 b). Modifying the timingdiagram of the register from continuous mode to burst mode changes theduty cycle from a high duty cycle to a low duty cycle. This allows forall the gates to be pinned to a low voltage for a significant length oftime, thereby making the MPP mode effective for such devices.

According to be another specific embodiment of the invention, the MPPmode is implemented in four-phase CCD output register by introducing anMPP barrier implant under two gates (instead of one) of the four phases.Referring to FIG. 13, the MPP barrier implant is under the gates φ_(H2)and φ_(H4) but not under the gates φ_(H1) and φ_(H3). This design allowsfor great flexibility in the operation of the output register. Theoutput register can be operated in a conventional four-phase clockingmode (as shown in FIG. 18). The output register can also be operated ina two-phase clocking mode by connecting two adjacent gates. With φ_(H1)and φ_(H2) connected to each other and φ_(H3) and φ_(H4) connected toeach other, the output register moves charge from right to left (seeFIG. 18). With φ_(H1) and φ_(H4) connected to each other and φ_(H2) andφ_(H3) connected to each other, the output register moves charge fromleft to right (see FIG. 18). This design combines the simplicity ofoperation of a two-phase output register (two input clocks instead offour) with the flexibility of a four-phase output register(bi-directionality of charge transport).

Linear CCDs have been designed historically for industrial and documentscanning applications and, as a result, have not benefited from some ofthe technology advances made with regard to scientific area CCDs. Forexample, linear CCDs feature high-speed readout amplifiers (e.g., thetwo-stage FET amp shown in FIG. 15 a) but not low-speed, low-noisereadout amplifiers. Therefore, the present invention provides a linearCCD for use with various embodiments using a low-speed low-noiseamplifier (e.g., a single-stage FET amp) (FIG. 15 b). The purpose ofthis design is to achieve a readout noise close to 10 electrons at 500kHz as compared to the readout noise of a conventional linear CCD whichis close to 300 electrons at 5 MHz.

The above-mentioned improvements are intended to improve the dynamicrange of linear CCDs. However, even with such improvements the dynamicrange of linear CCDs is still significantly lower than the dynamic rangeof photomultipliers. Therefore, in order to more closely match theperformance of laser scanning image plate readers (which utilizephotomultipliers), it is important to further increase the dynamic rangeof linear CCDs. A number of techniques are available to further increasethe dynamic range of linear CCDs. One such technique described in U.S.Pat. No. 5,055,667 consists of creating a nonlinear photosite response.

According to a specific embodiment of the invention, a technique isprovided in which the binning of the photodetector signals at the outputof the CCD register is dynamically controlled. Analog binning techniqueshave been used in the past to change the effective photodetector areaand overall resolution of CCDs. By contrast, in this embodiment, thebinning process is controlled “on the fly” to increase the dynamic rangeof the system as opposed to modifying its resolution. In a more specificembodiment, a linear CCD with four times as many photodetectors asrequired is used.

With conventional binning, the signals from four adjacent photodetectorsare combined systematically as they reach the output of the register,regardless of their signal value. Unfortunately, at high signalintensity, combining four signals can result in saturation of thereadout circuitry (i.e., an undesirable dynamic range limitation). Bycontrast and according to this embodiment, the signal of only onephotodetector is read out and compared to a threshold before deciding ifit will be combined with the signals of its three neighboringphotodetectors. If the signal value is below a certain threshold, thesignals of the following three photodetectors are binned with the signaljust measured, and the combined signal is re-measured.

If, on the other hand, the signal value is above a certain threshold, nobinning occurs and the signals of the following three photodetectors areeither discarded are read individually.

According to further embodiments, additional binning (e.g. combiningsignals from eight adjacent photodetectors instead of four) is effectedin order to further increase the sensitivity of the system, and thus thedynamic range. The term “dynamically-controlled binning” refers to thefact that binning only occurs for certain signal values and the decisionprocess is performed “on the fly”. This technique works particularlywell in this application because the signal values of neighboringphotodetectors are close to each other. This is due to the fact that thephotodetectors are small (˜20 μm) compared to the point spread functionof the storage-phosphor plate (˜120 μm).

According to a specific embodiment of the invention, a bilinear CCD isprovided (see FIG. 16) in which one shift register collects charges fromwide pixels 1602 (high sensitivity) and the other register collectscharges from narrow pixels 1604 (low sensitivity) interlaced with thewide ones. According to yet another embodiment of the invention, asingle shift register linear CCD is provided (see FIG. 17) in which oddpixels 1702 are narrow and even pixels 1704 are wide.

During the readout process, the narrow pixels are read first andcompared to a pre-determined threshold. If the pixel value is above thethreshold, the pixel value is validated and the associated wide pixel isdiscarded (i.e., it contains no information since it is saturated). Ifthe pixel value is below the threshold, the output amplifier is notreset, the associated wide pixel is binned with the narrow pixel, and acombined value is measured and validated. For low signal levels, noinformation is discarded and all the charges are read. For high signallevels, only a small fraction of the signal is read (ratio between thewidths of narrow and wide pixels) but this process does not introduceany additional noise. This readout process can result in significantincreases in the dynamic range of the device corresponding roughly tothe ratio of the alternating pixel sizes.

Similar binning techniques can be used with different pixelarchitectures as well as in the cross-scan direction. That is, the pixelvalue information along each line can be dynamically compared to apre-determined threshold to determine which mechanical scanning pitch isappropriate. If the signal levels are very low, a larger sampling pitchcan be used to maximize the sensitivity. If, on the other hand, thesignal levels are high, a smaller sampling pitch can be used to maximizethe spatial resolution. This dynamic resolution/sensitivity optimizationcan be implemented along the scanning direction as well as thecross-scanning direction. It should be noted that these dynamic rangeextension techniques are particularly important where the dynamic rangeof the CCD output amplifier has been intentionally reduced to maximizeits sensitivity.

Another unique CCD design feature is provided for use with variousembodiments of the invention, i.e., the photosensitive area is kept asclose as possible to the long edge of the chip since this edge definesthe boundary of the illumination area and therefore the area where thestimulated light is generated. Conventional linear CCDs have beendesigned for industrial and document scanning applications and thereforehave their photosensitive area placed in the center of the chip(typically 1 mm to 2 mm away from the edge). According to variousembodiments of the invention, the techniques developed for scientificbuttable area CCDs are utilized to manufacture a linear CCD which hasminimal dead space between its photosensitive area and three edges ofthe chip (e.g., typically less than 50 μm). The minimal dead space alongthe long edge facilitates maximum light collection. The minimal deadspace at each extremity of the linear array allowing the abutting ofmultiple arrays to create an uninterrupted photosensitive area.

The maximum length of a linear CCD array is determined by the size ofthe wafer on which it is manufactured. Typically 5″ or 6″ wafers areused to manufacture CCDs. This sets the practical limit for the lengthof the linear CCD below 4″. In order to read a standard 14″×17″ medicalplate in a single pass, it is necessary to mechanically butt a number oflinear CCDs. According to one embodiment, 4 mechanically-butted CCDs areemployed, each featuring a single row of 2048 pixels on a 44 μm pixelpitch. Each CCD is 9 cm long by 0.2 cm wide.

According to further embodiments, a special coating may be applied tothe photodetectors to bring the frontside quantum efficiency up to, forexample, 95% at 390 nm. Each CCD features two very low noisesingle-stage amplifiers (8 e⁻@ 30° C. & 400 kHz). The shift registerwell capacity is sized for optimal dynamic range and room temperaturedark signal. The CCD pixels may also be sized for optimal dynamic rangeand room temperature dark signal (for example 9 μm wide odd pixels and81 μm wide even pixels). Another specific embodiment for a linear CCD ispresented in FIG. 18.

The Filter Blocking Stimulating Light

A number of techniques have already been described herein for preventingthe stimulating light from reaching the linear array of photodetectors.According to further embodiments of the invention, additional steps maybe taken to block the stimulating light. According to such embodiments,multi-layer interference filters may be deposited on either or bothsides of the fiber-optic faceplate. According to more specificembodiments, an energy-absorbing material which absorbs electromagneticenergy at the wavelength of the stimulating light (e.g., red light) isadded to the optical cement which is used to bond the fiber-opticfaceplate to the linear array, or in the optical epoxy which is used asa transparent layer between the plate and linear array. A typical glueline thickness between the fiber-optic faceplate and the linear array is20 μm. If the glue line thickness is much thicker than 50 μm, a loss ofspatial resolution may occur.

Certain dye materials can be manufactured with extremely high absorptioncharacteristics (e.g. cyanines). Therefore, according to specificembodiments, such dyes are mixed in epoxy materials in highconcentration so as to absorb all the stimulating light within a verythin layer (e.g., less than 20 μm). One example of such a dye is aproduct manufactured by American Dye Source, Inc. (Quebec, Canada)referenced ADS 640HI and with the chemical formula C₃₉ H₅₅ N₂ I. Itsextinction coefficient is 200,000 /mol/cm at 643 nm. Its solubility isroughly 0.05 mol/l. For a 10 μm thickness (0.001 cm), the transmissionat 643 nm is therefore 10⁻¹⁰, which is sufficiently low to guaranteethat no stimulating light will reach the photodetectors

In addition, since some of these dyes are fluorescent (e.g., laserdyes), further embodiments of the invention provide additional absorbingmaterial in the epoxy to block the fluorescent light created by thefluorescent dye.

According to other embodiments, the chemical composition of the dye ischanged to quench its natural fluorescence. Quenching the fluorescenceof laser dyes in the red region of the spectrum has not previously beenachieved. Other techniques have been used to circumvent this problem.For example, European patent application EP 1 065 525 A2 describes amethod for filtering out the fluorescence of the laser dye by combiningit with a conventional colored glass filter (e.g. 1 mm Schott BG39). Theconventional colored glass filter does block the fluorescence of thelaser dye but introduces an unacceptable additional thickness in theoptical path. It is desirable to eliminate the fluorescence withoutintroducing an additional filter layer.

Therefore, according to one embodiment of the present invention, thechemical composition of the laser dye is modified to stop it fromfluorescing. This goes against traditional approaches which have beenaimed at maximizing (rather than minimizing) the fluorescence of laserdyes in order to increase the laser efficiency. This embodiment is basedon the fact that certain infrared dyes do not fluoresce, such as the dyeADS812MI manufactured by American Dye Source. ADS812MI has a peakabsorption at 812 nm and the following chemical formula: C₄₀ H₄₀ Cl N₂I. It appears that the presence of chlorine in the molecule may relateto the fact that this dye does not fluoresce. Therefore, according tothis embodiment of the invention, chlorine is introduced into thechemical composition of the red dye (as a form of perchlorate forexample) to inhibit its natural fluorescence.

The Scanning Mechanism

One scanning mechanism for use with the present invention (e.g., readoutapparatus 504 and actuator 508 described above) is a bidirectionaltranslation stage on which the linear photodetector array and the row ofilluminating LEDs are permanently mounted. According to a specificembodiment and as previously described herein, the forward scanningdirection of the stage is used to read and erase the platesimultaneously, whereas the reverse scanning direction of the stage maybe used for additional erasing of the plate (if necessary) in additionto bringing the stage back to its starting position. Due to theasymmetrical stimulation of the plate (knife edge illumination), thereading of the plate can only occur in the forward scanning direction.As will be understood, various mechanisms may be employed to translatethe stage across the plate including, for example, a motorized leadscrew, a motorized belt, a magnetic linear motor, and an inchworm motor.

It is important to note that all of these stage translation solutionsallow for the outer dimension of the stage and scanning mechanism toremain below half an inch (½″) in thickness. This dimension is importantfor the embodiments of the invention intended to fit inside a cassettethe size of a conventional film cassette as described above withreference to FIG. 6. Such an accomplishment is particularly impressivewhen compared to current laser scanning reading apparatus which areroughly the size of a household refrigerator.

For lead screw or belt solutions, the motor (which drives the lead screwor the belt) can be fitted inside or outside the film-like cassette. Inembodiments where the motor is fitted inside the cassette, a smallelectric motor (e.g., Mabuchi motor reference FF-N30VA) may be usedsince its overall thickness does not exceed 10 mm (less than ½″). Suchlow-profile electric motors are commonly available since they are usedin numerous consumer electronic products (CD players, cassette players,etc.).

In embodiments (e.g., FIG. 19) where the motor 1902 is disposed outsideof the cassette 1904, it is mechanically linked to the lead screw 1906or the belt (not shown) using, for example, a flexible cable 1908. Adistance of a few feet between the cassette and the motor as shown inthe figure allows for the necessary clearance and facilitates theinsertion of the cassette in a standard “bucky” tray as radiographycassette trays are commonly known. According to a more specificembodiment, the mechanical link exits the cassette at one corner at a 45degree angle as shown in the embodiments of FIGS. 20 a and 20 b. Anotherembodiment connects the mechanical link to the cassette with a hingeassembly as shown in the embodiments of FIGS. 21 a and 21 b.

These embodiments are intended to allow the cassette containing thereadout mechanism of the present invention to fit in most x-ray buckysin portrait or landscape mode without any modifications to the buckys.It is important that while the cassette is inserted in the bucky thecable (which may contain both the mechanical link and the electricalconnections to the readout apparatus) exits the cassette withoutinterfering with the tray.

In addition, specific embodiments of the cassette of the presentinvention may be used in a conventional x-ray machine without modifyingthe x-ray beam collimation. According to such embodiments, the imagingarea read by the cassette of the present invention is maintained to bevery close to the imaging area of a standard film cassette employed bythe x-ray machine. According to such embodiments, the blind areabordering the imaging area of the cassette is maintained to be as smallas the blind area in a conventional film cassette. According to one suchembodiment, this is accomplished through the use of a lead screw or beltmade of radiolucent material (e.g., lead screw 1906). According toanother such embodiment, the lead screw or the belt is placed at thevery edge inside the cassette. For embodiments employing a magneticlinear motor (e.g., FIG. 22), a u-shaped magnet 2202 can be placed alongthe inside edge of the cassette 2204 and the translation stage can befitted with a linear motor actuator 2206.

The Housing of the System

As mentioned above and according to specific embodiments, the housing ofthe system of the present invention is intended to be substantiallyidentical in size to a conventional film cassette. In case of a 14″×17″cassette shown in FIG. 23, a three foot mechanical and electrical cable2302 is provided between the cassette 2304 and the motor housing (notshown) and a longer electrical cable (not shown) is provided between themotor housing and the QA station. In the case of an 18 cm×24 cm cassetteand a 24 cm×30 cm cassette shown in FIG. 24, the motor 2402 is attachedto the housing 2404. In all such embodiments, the cassettes can fit inconventional buckys without any electrical or mechanical modifications.

According to another embodiment, an x-ray detection sensor is providedinside the cassette to detect whether the cassette is being exposed tox-rays. Once the x-ray exposure has stopped as indicated by the outputof the x-ray detector, the start of the scanning process is triggered.This eliminates the need for a connection to and synchronization withthe source of x-rays. According to a more specific embodiment, the x-raydetector is a photodiode (either a discrete component or part of thelinear array) which receives the light generated by the prompt emissionof the storage phosphor plate due to the exposure to the x-rays.

According to yet another embodiment, an RF detection device is providedin the cassette for detecting RF ID tags in close proximity to thecassette. This embodiment facilitates automation of the patient ID inputprocess. Traditionally, the patient ID is entered into a workstation inthe reception area and later reentered at a dedicated workstation by thex-ray technologist. The purpose of this second workstation is to “flash”each x-ray with the name and ID number of the patient as well as thedate of the exam. According to the present invention, the patient isissued a wristband in the reception area which stores the patient's IDinformation. In this way, the patient may be automatically identified bythe cassette when the wristband get close enough, the patient IDinformation being transmitted to or read by the associated workstationfor immediate verification and inclusion with the stored image.

While the invention has been particularly shown and described withreference to specific embodiments thereof, it will be understood bythose skilled in the art that changes in the form and details of thedisclosed embodiments may be made without departing from the spirit orscope of the invention. For example, specific embodiments have beendescribed herein with reference to one-dimensional, e.g., line-by-line,stimulation and readout of storage media. However, it will be understoodthat the principles of the present invention may be applied in thecontext of two-dimensional, e.g., pixel-by-pixel, stimulation andreadout using, for example, a laser pencil beam rather than an array ofLEDs. And although embodiments have been described herein with referenceto storage-phosphor plates and digital radiography, it will beunderstood that the present invention is applicable to a variety ofstorage media and information capture technologies. For example, thetechniques described herein may be used in the field of autoradiographyfor radio isotopic gel and blot analysis. In addition, other wavelengthsof stimulating and stimulated light are contemplated. That is, forexample, instead of red stimulating and blue stimulated light, thestimulating light could be infrared and the stimulated light green.Therefore, the scope of the invention should be determined withreference to the appended claims.

1. An integrated x-ray image capture and readout system, comprising: acassette enclosure having a form factor corresponding to a standardradiographic film cassette, the form factor corresponding to a thicknessof the cassette enclosure of about 0.6 inches; a storage-phosphor plateoperable to capture incident x-rays corresponding to an image; astimulating light source operable to expose a first portion of a surfaceof the storage-phosphor plate to stimulating light; an array ofdetectors positioned to receive stimulated light via a second portion ofthe surface of the storage-phosphor plate adjacent the first portion ofthe surface, the stimulated light being released from thestorage-phosphor plate in response to a portion of the stimulating lightdiffused under the second portion of the surface of the storage-phosphorplate; and an actuator assembly operable to effect relative motionbetween the surface of the storage-phosphor plate and both thestimulating light source and the array of detectors in one dimension;wherein the array of detectors are positioned in sufficiently closeproximity to the surface of the storage-phosphor plate such that thestorage-phosphor plate, the stimulating light source, the array ofdetectors, and the actuator assembly are enclosed in the cassetteenclosure.
 2. The system of claim 1 further comprising an actuatordriver positioned externally to the cassette enclosure and operationallycoupled to the actuator assembly via a mechanical link.
 3. The system ofclaim 2 wherein the actuator driver is coupled directly to the cassetteenclosure.
 4. The system of claim 2 wherein the actuator driver isseparate from the cassette enclosure.
 5. The system of claim 2 whereinthe mechanical link connects the actuator driver and the actuatorassembly via an aperture at a corner of the cassette enclosure.
 6. Thesystem of claim 5 wherein the mechanical link forms a 135 degree anglewith each of two edges of the cassette enclosure joined at the corner.7. The system of claim 5 wherein the mechanical link is hinged at thecorner of the cassette enclosure to allow at least lateral movement ofthe mechanical link.
 8. The system of claim 2 wherein the array ofdetectors is operable to convert the stimulated light to electronic datacorresponding to the image, the system further comprising a transmissionmedium for transmitting the electronic data out of the cassetteenclosure, the transmission medium exiting the cassette enclosure viathe aperture.
 9. The system of claim 1 wherein the actuator assembly isdisposed along an edge of the cassette enclosure to maximize an imagingarea of the storage-phosphor plate.
 10. The system of claim 1 wherein atleast a portion of the actuator assembly comprises a radiolucentmaterial.
 11. The system of claim 1 wherein the actuator assemblycomprises one of a lead screw, a belt, a magnetic linear motor, and aninchworm motor.
 12. The system of claim 1 wherein the array of detectorsis operable to convert the stimulated light to electronic datacorresponding to the image, the system further comprising a transmissionmedium for transmitting the electronic data out of the cassetteenclosure.
 13. The system of claim 1 further comprising a radiofrequency detector for detecting radio frequency energy in closeproximity to the cassette enclosure, the radio frequency energycorresponding to patient information to be associated with the image.14. The system of claim 13 further comprising a radio frequencytransmitter disposed outside of the cassette enclosure for generatingthe radio frequency energy.
 15. The system of claim 14 wherein the radiofrequency transmitter is included in one of a wrist band and a badge.16. The system of claim 1 further comprising an image capture detectioncircuitry for sensing whether capture of the incident x-rays isoccurring and generating a signal indicative thereof.
 17. The system ofclaim 16 wherein the image capture detection circuitry comprises anx-ray detector for detecting some of the incident x-rays.
 18. The systemof claim 16 wherein the image capture detection circuitry comprises aphotodiode for detection prompt emission of the storage-phosphor platein response to the incident x-rays.
 19. The system of claim 16 whereinthe signal is employed to control actuation of the actuator assembly.20. The system of claim 1 wherein the actuator assembly comprises amagnetic linear motor and the stimulating light source and the array ofdetectors are configured on a translation stage.
 21. The system of claim20 wherein the magnetic linear motor comprises at least one magnetdisposed inside and along an edge of the cassette enclosure, and alinear motor actuator coupled to the translation stage.
 22. The systemof claim 1 wherein the form factor of the cassette enclosure correspondsto a standard radiographic film cassette having a set of dimensionscorresponding to one of 14″×17″, 14″×14″, 10″×12″, 8″×10″, 35 cm×43 cm,35 cm×35 cm, 20 cm×40 cm, 18 cm×43 cm, 13 cm×18 cm, 13 cm×30 cm, 18cm×24 cm, or 24 cm×30 cm.